Alloy addition agent



ALLOY ADDITION AGENT.

Donald. C. Hilty, NiagaraFalls, N. Y., assignor toUnion Carbide and Carlton Corporation, a corporation of New York No Drawing.v Application November'26, 1952, SerialNo. 322,817

.Claims. (Cl. 75-27) This. invention relates. to. an exothermic agent suitable for use. in adding alloying materials, particularly chromium, to steeland for adding heat to molten iron. orsteel toi facilitate the addition of alloying elements to such metals.

In the steel making. art, the use of exothermic mixturesfor adding alloying materials to steel is well known. Conventionally, pellets containingthe alloying material, an oxidizing agent, and a reducing agent are prepared andadded tothe ladle during or after the pouring of the steel. The oxidizing and reducing agents are selected so that at the temperature of the molten steel the two will react exothermically. The heat from this exothermic reaction facilitatesthe solution of, the alloying material in the steel. A proper choice of an oxidizing and a reducing agent insures the liberation of enough heat to permit the solution of the alloying material in a relatively short period of time and to prevent the excessive loss of heatduring the time required for the alloying material to go into solution. If the alloying material dissolves too slowly and too much heat is lost, poor recovery and segregation of the alloying material in the steel result.

Several combinations of oxidizing and reducing agents have been proposed by the prior art for incorporation in an exothermic mixture containing an alloying material. One of the most common reducing agents suggested is silicon. Potassium chlorate and sodium nitrate are examples of the many oxidizing agents employed.

Potentially the exothermic reaction between silicon and potassium perchlorate is one of the most useful available for the addition of alloying elements. However, a pellet consisting of silicon, potassiumperchlorate, and an alloying material, such as low-carbon ferrochrome, willfioat on a body of molten steel until it slowly dissolves. The conditions usually existing when such additions are made are not proper for initiating the exothermic reaction between the silicon and the potassium perchlorate.

It is the principal object of the invention to provide an exothermic addition agent in which potassium perchlorate and silicon are, respectively, the oxidizing and re ducing agents.

In a c'opending application, Serial No. 254,796, filed November 3, 1951, now Patent No. 2,628,898 issued February 17, 1953 by the present applicant, an exother'r'nic mixture comprising specified proportions of silicon, potassium perchlorate, and soda ash was disclosed. Soda ash acts as an accelerator in the mixture and causes the silicon and potassium perchlorate to react exothermically under the conditions prevailing when the mixture is added to a bath of molten steel.

It has now been discovered that calcium-aluminate is elfective as an accelerator in bringing about the exothermic reaction between silicon and potassium perchlorate. According to the present invention, a mixture contailiing an alloying material, such as ferrochromium, silicon, potassium perchlorate, and calcium-aluminate can be used for making additions of alloying elements to steel; The potassium perchlorate shouldbe present in an r 2,776,203 Patented Jan. 1, 1957 2 amount equal to from 1.5% to 15% of the mixture, At least 0.5% of the mixture should be silicon and silicon should be present in such greater amount as is necessary to make the atomic ratio of silicon to the. oxygen. in the, potassium perchlorate at least 0.5. Calcium-aluminate should be present in an amount not less than 0.5 of the mixture and preferably between 1% and 7.5%v of the mixture. Best results have been obtained with mixtures containing from about 2% to 5% calcium-aluminate.

Certain advantages are realizedwhen calcium-aluminate rather than soda ash is the accelerator in the mixture. With calcium-aluminate the amount of carbon added. to. the steel is quite low, being limited to the amount of carbon in the alloying material. With soda ash some carbon from the soda ash itself is introduced into the steel. This carbon addition from the soda ash, while small, can cause considerable. trouble when low carbon steels, for example those having 0.03% maximum carbon, are being made. For this reason the exothermic mixture of the present invention has been found to be particularly useful in making steels having a low or critical carbon content. Of course, theexothermic mixture of the. invention is not limited to such uses.

Preferably the mixture of the invention is prepared in pelleted formfor convenience in handling. Conventional. pelleting techniques, are suitable for this purpose. For, example, the exothermic alloy addition agent of the invention can be pelleted by comminuting the constituents, mixing them, adding a little water and compressing the, mixture into pellets on a hydraulic press, A binder may beused to strengthen the pellets providedthebinder does not interfere with the exothermic reaction; Small quantities. of sodium carbonate, for example, when blended, with the reactants prior to pelleting, impart added; strength to.the pellets. The mixture or pellet should-be reasonably homogenous, but nospecial blending techniques are required to make a satisfactory exothermic mixture within the scope of this invention,

The choice of theproper amounts of theconstituents within the limits set forth above is based largely upon the requirements of the particular job to be accomplished, In general the greater the amount of exothermic mate.- rials present in the mixture the smaller the drop in temperature ofthe molten steel. Also, some increaseis ob: tained in the rate of solution of the alloying materials when the amount of exothermic reactants is increasedabove the minimums specified. j

The principal constituents of the calcium-aluminate accelerator are the oxides of calcium andaluminurn. The limeor calcium oxide content of the accelerator should be about to 30% by weight. Alumina or aluminum oxide should constitute from about 30% to 70% by weight of the accelerator. Iron oxide, FezOs, can. be

substituted. for a part of. the alumina in which, case. the

sum of the F6203 and A1203 in the accelerator should be from about 30% to 70% with nornore than 20% of: the accelerator being iron oxide. Impurities such as silica, magnesia, barium oxide, manganese oxide, and the oxides of the alkali metals can be present in the accelerator in amounts up to 10% by weight without detrimentally affecting the accelerator.

One common source of a suitable calcium-alumirrateis furnace slag. A cement sold under the name of Atlas Lumnite has also given good results. This cement has an approximate composition of 40% CaO, 40% A1203, 15%, FezOs, and 5% incidental impurities such as magnesia and silica.

The silicon in the mixture maybe present in elemental term or as an alloy of either iron or one of the other alloying materials. Ferrosilicon, silicon bearing fen-o;

chrome, or ferrochrome-silicon are examplesof; suitable silicon containing materials.

In one test of the mixture of the invention, about 5% chromium was added to one hundred pounds of molten steel in an induction furnace. The addition was made in the form of pellets containing 88% silicon-bearing lowcar bon .ferrochromium (about 6% silicon), potassium perchlorate, and 2% calcium aluminate slag. The calcium .alumin-ate slag had a composition of about 40% CaO, 52% A1203 and 8% MgO and incidental impurities.

The chromium dissolved in the steel within 65 seconds. The temperature of the molten steel was 1'619 C. before and 1615 C. after the addition. No appreciable segregation of the chromium occurred. Changes in the percentages of carbon, silicon, and chromium due to the addition of the mixture of the invention are set forth in Table I.

The total chromium added in the above test was 4.69% based on calculations. Since the analyses reported in Table I indicated an increase in the chromium content of the steel of 4.42%, it can be seen that the recovery of the chromium in the steel was quite high.

Pellets similar to those used in the previous test were used to add about 1% chromium to one hundred pounds of molten steel. The chromium dissolved in 30 seconds with no measurable change in the temperature of the steel. In this test the calculated amount of chromium added to the steel was 1.04% and the increase in the chromium content of the steel was shown by analyses to be 1.03%.

Pellets of the invention containing either the calcium aluminate slag described above or Lurnnite cement as the accelerator were made up for purposes of comparison. Additions of 100 grams of chromium were made to one hundred pounds of molten steel. The pellet containing 5% of the calcium aluminate slag dissolved in 30 seconds. The pellet containing 5% of the Lumnite cement dissolved in 40 seconds. While in this instance the pellet with Lumnite cement took longer to dissolve than did the one with calcium aluminate slag, the time required was not excessive and the finished steel showed no signs of segregation when the Lumnite cement was MSGd.

In another series of tests, pellets containing ferrosiliconchrome were made and added to molten steel. The ferrosilicon-chrome had an approximate composition of 54% chromium, 29% silicon, iron, remainder incidental impurities. The pellets tested also contained 5% potassium perchlorate and 5% calcium aluminate slag as an accelerator. One percent additions of chromium were made to one hundred pounds of molten steel with the results given in Table II.

TABLE II Time to Temperw Test Dissolve ture Change (seconds) C.)

4; suitable materials for imparting to the mixture the desired amount of the alloying element. The alloying element may however be present in the mixture in any of the forms conventionally employed by the art for making alloy additions to steel.

The sizes of the particles in the mixture have not been found to be critical. Of course, as is true in any instance in which the reactants involved are solids, the reactivity of the mixture is improved up to a point by the reduction of the size of the particles. Particles which pass through a one hundred mesh screen (0.149 mm. opening) have given excellent results. Some improvement was observed in the performance of the pellets containing the ferrosilicon-chrome when the particle size in the pellet was reduced so that about 75% of the particles passed through a 200 mesh screen (0.074 mm. opening). Such adjustments in the size of the particles in the mixture as may be desirable are within the skill of the ant.

According to one aspect of the invention, a mixture of silicon, potassium perchlorate, and the calciumaluminate accelerator may be used to add heat to molten metal during the time when separate pellets of alloying metals are being added or while the molten metal is merely standing. The exothermic mixture is of course preferably pelleted in the same manner as the exothermic alloying mixture of the invention. In tests similar to those reported in Tables I and II, one percent additions of manganese in the form of low carbon ferromanganese were made to one hundred pound heats of steel. When the ferromanganese was added to the heat one hundred and eighty grams of the exothermic pellets were also added. The data from these additions .are tabulated in Table III.

The exothermic mixture should have a minimum calcium aluminate content of 2% of the combined weights of silicon and potassium perchlorate. Smaller amounts have been found to give unsatisfactorily slow reaction rates or no reaction at all. No particular advantage is obtained with more than 7.5% calcium aluminate. Silicon should be present in the mixture in an amount not less than 15 Potassium perchlorate should be present in the mixture in an amount sufficient to make the atomic ratio of silicon to the oxygen in the potassium perchlorate at least 0.5. Smaller amounts of the potassium perchlorate will result in the addition of silicon to the steel or, if insufiicient potassium perchlorate is present, an unsatisfactory exothermic reaction. If an excess of the potassium perchlorate is present the iron or steel as well as other elements present in the heat may be oxidized.

For best results the exothermic mixture of the invention which does not contain an element to be alloyed with the iron or steel should have the following composition: 30% to 60% ferrosilicon having a silicon content such that at least 15% of the mixture is silicon, to 40% potassium perchlorate and at least 2% calcium aluminate. The preferred exothermic mixture has the following composition: 54% potassium perchlorate, 44% ferrosilicon (silicon comprising 50% of the ferrosilicon) and 2% calcium aluminate.

What is claimed is:

1. An exothermic alloy addition agent consisting of silicon, potassium perchlorate, and calcium-aluminate, said silicon being present in an amount equal to at least 15% of said mixture, the proportions of silicon and potassium perchlorate in said mixture being such that the atomic ratio of silicon to the oxygen in the potassium perchlorate is at least 0.5, said calcium-aluminate being present in an amount equal to at least 2% of the combined Weights of silicon and potassium perchlorate, the remainder being alloying elements, iron and incidental impurities.

2. An exothermic alloy addition agent consisting of ferrosilicon, potassium perchlorate and calcium-aluminate, said ferrosilicon having a silicon content such that at least of said mixture is silicon, the proportions of silicon and potassium perchlorate in said mixture being such that the atomic ratio or" silicon to the oxygen in the potassium perchlorate is at least 0.5, said calcium-aluminate being present in an amount equal to at least 2% of the mixture, the remainder being alloying elements and incidental impurities.

3. An exothermic alloy addition agent consisting of to of ferrosilicon having a silicon content such that at least 15% of the mixture is silicon, to 40% of potassium perchlorate, and at least 2% calcium-aluminate, the remainder being alloying elements and incidental impurities.

4. An exothermic alloy addition agent consisting essentially of 1.5% to 15% potassium perchlorate, silicon being present in an amount of at least 0.5% and in such greater amount as is required to provide an atomic ratio of silicon to the oxygen in the potassium perchlorate of at least 0.5, at least 0.5% calcium-ahuninate, the remainder being alloying elements.

5. An exothermic alloy addition agent as claimed claim 4 wherein the alloying material contains chromium.

6. An exothermic alloy addition agent as claimed in claim 4 wherein the alloying material is low carbon ferrochromium.

7. An exothermic alloy addition agent consisting essentially of 1.5 to 15% potassium perchlorate, silicon being present in an amount of at least 0.5% and in such greater amount as is required to provide an atomic ratio of silicon to the oxygen in the potassium perchlorate of at least 0.5, 1% to 7.5% calcium-aluminate, the remainder being an alloying material.

8. An exothermic alloy addition agent as claimed in claim 7 wherein the alloying material contains chromium.

9. An exothermic alloy addition agent as claimed in claim 7 wherein the alloying material is low carbon ferrochromium.

lO. An exothermic pellet consisting essentially of 1.5% to 15% potassium perchlorate, silicon being present in an amount of at least 0.5% and in such greater amount as is required to provide an atomic ratio of silicon to the oxygen in the potassium perchlorate of at least 0.5, at least 0.5% calcium-aluminate, a binder, the remainder being alloying elements.

References Cited in the file of this patent UNITED STATES PATENTS 2,247,262 Udy June 24, 1941 2,628,898 'Hilty Feb. 17, 1953 2, 4 Ti m s n Ja 95. 

1. AN EXOTHERMIC ALLOY ADDITION AGENT CONSISTING OF SILICON POTASSIUM PERCHLORATE, AND CALCIUM-ALUMINATE, SAID SILICON BEING PRESENT IN AN AMOUNT EQUAL TO AT LEAST 15% OF SID MIXTURE, THE PROPORTIONS OF SILICON AND POTASSIUM PERCHLORATE IN SAID MIXTURE BEING SUCH THAT THE ATOMIC RATIO OF SILICON TO THE OXYGEDN IN TH POTASSIUM PERCHLORATE IS AT LEAST 0.5, SAID CALCIUM-ALUMINATE BEING PRESENT IN AN AMOUNT EQUAL TO AT LEAST 2% OF THE COMBINED WEIGHTS OF SILICON AND POTASSIUM PERCHLORATE, THE REMAINDER BEING ALLOYING ELEMENTS, IRON AND INCIDENTAL IMPURITIES. 